In the operation of prior art tandem rolling mills it has been necessary to roll the entire length of metal strip material on one coil to a single specified thickness. That is, there had been no satisfactory way of changing gauge while the strip material was in motion.
U.S. Pat. No. 3,807,206 to Connors for "Strip Gauge Change During Rolling in a Tandem Rolling Mill" provided one solution for changing gauge under dynamic conditions. According to the teachings of this patent the speed and roll gauge setting of the first stand are changed. Thereafter in timed sequence the roll gap settings and speeds of succeeding stands are changed until all roll gap settings and speeds of the stands in the mill have been changed to accommodate a new gauge rolling schedule.
U.S. Pat. No. 3,852,983 to Cook for "Work Strip Gauge Change During Rolling in a Tandem Rolling Mill", addressing itself to the same problem, proposes to make the changes in stand speed and roll gap setting in a different manner. Cook teaches the utilization of a precalculated per unit multiplier to successively and progressively change the mill stand speeds of all the stands save the pivot stand, the speed of which remains constant at the previously scheduled rate. Interstand tension regulators between the stands automatically change the gauge at the stand of entry of the gauge change point of the moving strip of material.
The present invention provides an analog stand speed reference circuit to realize the teachings of Cook, and insure that the changes in stand speed are made at the same rate and at the same time in order to prevent spurious interstand tensions from developing. For example in a five stand mill at the gauge change transition at stand 3, the speeds of stands 1 and 2 are changed and the gauge but not the speed at stand 3 is changed. If the speed changes at stands 1 and 2 are not made at the same time and the same rate, a spurious interstand tension will develop between stands 1 and 2 and the interstand tension regulator will attempt to change the roll gap opening at stand two. Since the roll gap opening at stand two had already been changed to its proper and new schedule magnitude, this would result in a hunting of the interstand regulators and cause off gauge material to be rolled. The present invention insures that the speed changes are made at the same time and in unison.